Energy saving and pollution reduction considerations, above all in the urban environment, are leading motor vehicle manufacturers to equip the models thereof with an automatic start/stop system, such as a “Stop and Go” system.
As the company VALEO EQUIPEMENTS ELECTRIQUES MOTEUR states in patent application FR2875549, the vehicles are made capable of operating according to the “Stop and Go” mode as a result of a reversible electric machine, or starter-alternator, coupled with the thermal engine.
The use of a starter-alternator in a “Stop and Go” operating mode consists, under certain conditions, in causing the thermal engine to stop completely when the vehicle itself has stopped, then restarting the thermal engine following, for example, an action by the driver interpreted as a restart request.
A typical “Stop and Go” situation is stopping at a red light. When the vehicle stops at the lights, the thermal engine is automatically stopped, then, when the light turns green, the engine is restarted by means of the starter-alternator, following the detection by the system of the driver pressing the clutch pedal, or of any other action conveying the wish of the driver to restart the vehicle.
To this end, as also indicated by the company VALEO EQUIPEMENTS ELECTRIQUES MOTEUR in patent application FR2875551, the “Stop and Go” system uses information representative of the operational state of the vehicle, which information is provided by the vehicle sensors, such as the sensors for the passenger compartment temperature or for detecting the position of the clutch pedal, or the information read on a data communication bus, such as the speed of the vehicle or the rotational speed of the engine.
Such an automatic start/stop system is, to date, only provided in private cars, yet the advantage thereof is well understood in terms of energy saving and environmental projection, taking into account town traffic conditions.
However, another source of pollution is the diesel engines of commercial vehicles, in particular those of buses and other service vehicles.
Some local authorities have therefore adapted their vehicle fleets to fuels other than gas oil, that are less polluting, such as LPG, ethanol or even hydrogen.
The fact remains that a bus carries out a number of stops and that the engine needlessly consumes fuel during the time that passengers get on and off.
It is therefore natural to envisage installing a “Stop and Go”-type system so as to reduce the average fuel consumption of a bus.
However, buses, as well as some heavy goods vehicles, have specific safety and driving assistance systems that private vehicles do not have.
In particular, the EAB, abbreviation for “Exploitation Assistance Brake” is a braking system, which allows the vehicle to be held back when the driver releases his/her foot from the service brake (footbrake) even when in gear.
When stopping at a red light, or during another prolonged stop, the driver generally applies a large pressure on the brake pedal so that the vehicle does not move forward. The EAB overcomes this requirement by applying the brakes, as explained in detail, for example, in document U.S. Pat. No. 3,905,651.
It also has another function, which is dedicated to public transport: it allows the back doors to be unlocked. Indeed, the bus driver cannot unlock the passenger doors without activating the EAB.
On all of these vehicles, the safety brake is activated as soon as the EAB is engaged.
On some vehicles, it is even possible to pre-activate the EAB before coming to a stop. This is extremely practical for preventing loss of time, but requires knowledge of other vehicle parameters in order to authorise the thermal engine to stop (for example: the vehicle speed, etc).
The EAB also enables the automatic gear box to be returned to neutral to prevent it becoming needlessly heated during stop stages.
The EAB also helps prevent lapses of concentration by the driver resulting in an accident. On some vehicles, when the EAB is engaged, even if the driver presses on the accelerator, nothing happens and no order is sent to the computer.
It further enables, on some buses, the vehicle to be slowed without the accelerator necessarily being released, or the air suspensions to be stiffened so as to make it safe for passengers to get on and off.